WaveNet isn't just for speech either: it can also generate some styles of music. Training the network on classical piano, for example, yielded some uncannily cohesive chord progressions in the researchers' testing.

But even weirder is what happens when the system isn't told what to do. Since WaveNet is autoregressive, it can still generate a voice even if it isn't given any text input, resulting in a predictive “babbling” that sounds like Siri practicing her glossolalia. The researchers also found that the system is eerily adept at picking up on non-verbal speech characteristics, like breathing and mouth movements.